A seat belt buckle devised to maximize holding capability as well as to improve the cost and ease of manufacture is disclosed in the U.S. Pat. No. 4,617,705 issued to James R. Anthony and Allan R. Lortz. The buckle includes a reinforcement plate mounted to and between an upper and lower housing containing a spring biased pawl engageable with a seat belt tongue. The pawl is held captive between the lower housing and the reinforcement plate, and is biased upwardly against the plate by a pair of springs. A push button is slidably mounted to the upper housing and has a pair of legs extending downwardly through the plate to contact and move the pawl downwardly to disengage the pawl from the tongue. An additional spring mounted between the push button and reinforcement plate requires force above a predetermined level to move the button downwardly and to disengage the pawl from the tongue. In many cases, the seat belt tongue is split into two separate tongues for attachment respectively to a seat belt and a shoulder harness. It is desirable to provide such a belt buckle having a pair of tongues interlockable together, but easily separable to facilitate disengagement of the belt and harness with the user.
False latching between a belt buckle and associated tongue must be avoided. In the case of a belt buckle engageable with a pair of tongues, the buckle must be designed so that it will not lockingly engage when only a single tongue is inserted into the buckle. We have therefore devised a belt buckle which will lockingly engage the tongues only when both tongues are fully inserted therein.
When utilizing a pair of tongues in combination with a buckle, it is easy to insert one or more of the tongues in an incorrect manner. For example, a tongue could be inserted upside down thereby causing twists in the seat belt or shoulder harness. We have therefore designed the interface between the tongues and buckle to allow insertion of the tongues only in the correct manner.